The Proton Radius Puzzle

Dr. Mahbub Khandakar
Department of Physics
Idaho State University


The proton charge radius (rp) is one of the most fundamental quantities in physics. Precise knowledge of its value is critically important for both nuclear and atomic physics - particularly for the spectroscopy of atomic hydrogen, and rp is a crucial input to high precision tests of quantum electrodynamics (QED).  Recent very high precision measurements of rp using the muonic hydrogen atom have demonstrated up to eight standard deviations smaller value than the accepted average from all previous experiments performed with different methods.  This fact triggered the well-known “proton radius puzzle” in hadronic physics. The PRad collaboration at Jefferson Lab for the last five years has developed a novel magnetic-spectrometer-free elastic electron-proton scattering experiment to address this puzzle.  The PRad experiment was successfully performed in May and June of 2016 at Jefferson Lab in which a large statistical and high quality experimental data set was collected. The specifics of the experimental method and the characteristics of the setup together with the first preliminary results from the initial analysis of the collected data will be presented in this talk.